Ourstudy has shown that the inability of ecf mutants of E. coli to couple metabolic energy to active transport of amino acids and some sugars is due to a markedly reduced ability in maintaining the electrochemical gradient of protons without there being an increased membrane permeability to protons. Study on other ecf mutants indicates strongly that the electrochemical gradient of protons is in itself insufficient as the immediate driving force for active transport. Work is now in progress in identifying the ECF protein. There is also a strong indication that the ECF protein is required for oxidative phosphorylation. Work is now in progress in obtaining genetic evidence for the possible physical interaction of the ECF protein and the Ca, Mg-ATPase.